How to create a "Time Counter" variable?

How to create a "Time Counter" variable?

Hello,
As the title, How to create a "Time Counter" variable? When the event is active, the Time Counter variable runs; and when the event is inactive, the Time Counter is reset to zero.
Regards,
Peng

This is a migrated post! Originally posted on 24.08.2009 by user lephis. Please be aware that information can be outdated.